Aircraft having helicopter rotor and front mounted propeller

ABSTRACT

An aircraft features a nose mounted propeller on a fuselage having a typical helicopter rotor assembly. By reducing the amount of forward thrust needed from the main rotor, the propeller allows greater forward speeds as the angle of attack on the rotor&#39;s blades can be kept low to avoid the stalling and violent vibration experienced by conventional helicopters at relatively high speeds. By greatly reducing the amount of thrust produced by the main rotor but still using it to generate lift, the addition of wings can be avoided. The aircraft can be flown in a forward direction in a generally horizontal orientation, as the nose does not have to be pitched downward to create thrust from the main rotor.

This application is a continuation-in-part of application Ser. No.11/259,353 filed Oct. 27, 2005.

The present invention relates to an aircraft and more particularly to anaircraft having a fuselage with a helicopter rotor supported on the topand a propeller mounted on the front for providing forward thrust.

BACKGROUND

Conventional helicopters, while offering drastically improvedmanoeuvrability over airplanes, are limited to travelling at relativelylow speeds. During vertical motion or hovering, the helicopter isoriented horizontally such that the main rotor is driven for rotationabout a generally vertical axis to create lift. To achieve forwardmotion, extra power is applied, collective pitch is increased and thehelicopter is tilted nose down out of the horizontal orientation byadjusting the cyclic pitch to increase the angle of attack of the rotorblades during a portion of their rotation in which they extend rearwardfrom the hub, thereby create more lift near the rear of the aircraft.With the aircraft in this tilted position, the rotor acts to create bothlift and forward thrust.

During forward flight, the effective air speed of a blade as it advancesin its rotation is the sum of the forward speed of the helicopter andthe blades rotational speed, as the motion of the blade relative to thehelicopter is in a forward direction. The effective air speed of aretreating blade however, is the difference between the rotational speedand the forward speed of the helicopter, as they are in oppositedirections. Since lift varies with the square of velocity, the advancingblade will thus produce more lift than the retreating blade. Thisdissymmetry of lift can be counteracted by flapping and cyclicfeathering of the blades, which increase and decrease the angles ofattack of the retreating and advancing blades respectively duringforward flight to create a balance of lift between the two sides.Increasing the angle of attack too much will cause a blade to stall, assmooth laminar airflow over the surfaces of the blade is lost. As thecritical angle of attack is approached, the blades undergo violentvibrations known as buffeting. As a result, conventional helicopters arelimited in their maximum speed as increasing the forward velocity leadsto a need for increased angle of attack for retreating blades, and ahigh angle of attack will lead to stalling and a corresponding lack oflift.

Compound helicopters have been developed to try and overcome the speedlimitations of conventional helicopters. These compound aircraft combinefeatures of the helicopter with those of an airplane in an attempt toprovide the manoeuvrability of the former and the speed of the latter.U.S. Pat. Nos. 2,531,976 and 2,575,886 by Garrett and Myers respectivelyand U.S. Patent Application Publication Number 2005/0151001 by Loperdescribe compound helicopters that have wings and nose mountedpropellers that provide lift and thrust respectively for forward flightat speeds that could not be achieved using their main rotors. Garrettteaches a main rotor assembly that is folded down into a fuselage of theaircraft during forward flight. Myers teaches a main rotor that isstopped in a position parallel to the line of flight when approachingthe stalling speed so as not to create drag during forward flightprovided by the propeller and wings. Loper teaches a main rotor that isunloaded to autogyrate during cruising flight so that the majority oflift is provided by the wings. The presence of wings on these aircraftdecrease the efficiency of using the main rotor to create lift duringvertical movement, hovering and the transition from hovering to forwardflight as their surface area creates vertical drag. Wings also increasethe weight of the aircraft and the cost of its manufacture due to morematerial and assembly requirements. The wings of a compound helicopterdo not automatically eliminate all rotor related issues in forwardflight. For example, in compound helicopters with the rotor arranged tofree-wheel in forward cruising, the weight and drag created by thefree-wheeling rotor still have to be dealt with.

As a result, there is a desire for a rotor-based aircraft capable ofhigher forward cruising speeds than a conventional helicopter withoutrequiring the addition of wings below the main rotor.

SUMMARY

According to a first aspect of the present invention there is providedan aircraft comprising:

a fuselage having a front end and a longitudinal axis;

a main helicopter rotor supported for rotation about an axis thereof ontop of the fuselage, said rotor being operable to control both verticaland horizontal movement of the aircaft;

a propeller supported for rotation about an axis thereof at the frontend of the fuselage for selectively producing thrust to move theaircraft forward; and

at least one powerplant supported on the fuselage;

the main rotor and propeller each being operatively connected to the atleast one powerplant for selective driven rotation thereby;

wherein on at least one side of the fuselage, vertical lift is providedsubstantially wholly by the main helicopter rotor during forward flight.

The present invention provides a nose mounted propeller on a fuselagehaving a typical helicopter rotor assembly that can be adjusted by thepilot to provide vertical lift and horizontal thrust in forward,rearward and transverse directions. By reducing the dependency on themain rotor for forward thrust, the propeller allows greater forwardspeeds as the angle of attack on the rotor's blades can be kept low toavoid the stalling and violent vibration experienced by conventionalhelicopters at relatively high speeds. By greatly reducing the amount offorward thrust produced by the main rotor but still using it to generatelift, the addition of wings can be avoided.

The at least one powerplant may comprise a propeller powerplant and arotor powerplant, the propeller and main helicopter rotor beingoperatively connected to the propeller and rotor powerplantsrespectively. Alternatively, the at least one powerplant may comprise acommon powerplant having a rotor output and a propeller output, thepropeller and main helicopter rotor being operatively connected to thepropeller and rotor outputs respectively.

The propeller may be adjustable in pitch. Alternatively, there may beprovided a clutch operable to couple and decouple the propeller and theat least one powerplant. Minimizing the propeller pitch or disengagingthe clutch during hover prevents interference with operation of the mainrotor by the propeller to allow stable hover.

Preferably the main helicopter rotor, at a forwardmost point of itsrotation, and the propeller,-at an uppermost point in its rotation, movein a common direction. In other words, the main helicopter rotor andpropeller, as viewed from above the aircraft and the rear end of theaircraft respectively, rotate in a same one of clockwise andcounter-clockwise directions. In this instance, preferably the propelleris supported for rotation in a plane generally perpendicular to arotational plane of the main helicopter rotor. There may be provided ahorizontal stabilizer disposed rearward of the fuselage and extendingobliquely with respect to the longitudinal axis of the fuselage so as toextend downward from front to rear. The horizontal stabilizer may besupported rearward of a tail rotor supported for rotation rearward ofthe fuselage. With the relationship between the rotational directions ofthe main rotor and propeller defined such that they move in the samedirection as indicated above, the aircraft may have a tendency to pitchnose-up with the propeller powered to create forward thrust. Thedownward angling of the horizontal stabilizer creates lift at the tail,thereby acting to counter this nose-up tendency during forward flight.

Alternatively, the main helicopter rotor, at a forwardmost point of itsrotation, and the propeller, at an uppermost point in its rotation, movein opposite directions. In other words, the main helicopter rotor andpropeller, as viewed from above the aircraft and the rear end of theaircraft respectively, rotate in opposite ones of clockwise andcounter-clockwise directions. In this instance, preferably the propelleris supported for rotation in a plane transverse to the fuselage andinclined with respect to the longitudinal axis of the fuselage.Alternatively there may be provided a horizontal stabilizer disposedrearward of the fuselage and extending obliquely with respect to thelongitudinal axis of the fuselage so as to extend upward from front torear. The horizontal stabilizer may be supported rearward of a tailrotor supported for rotation rearward of the fuselage. With therelationship between the rotational directions of the main rotor andpropeller defined such that they move in opposite directions asindicated above, the aircraft may have a tendency to pitch nose-downwith the propeller powered to create forward thrust. The tilting of thepropeller or horizontal stabilizer may help counteract this tendency.

There may be provided a wing extending laterally from one side of thefuselage to counter dissymmetry of lift of the main helicopter rotorduring forward flight. By providing lift on a side of the aircraftopposite the advancing blade, the wing reduces reliance on increasingthe angle of attack of the retreating blade to counter dissymmetry oflift of the main rotor. This aids in keeping the main rotor's angle ofattack low to allow faster forward speed without retreating blade stall.

According to a second aspect of the invention there is provided a methodof flying an aircraft comprising a fuselage having front and rear endsand a longitudinal axis, a main helicopter rotor supported for rotationabout an axis thereof on top of the fuselage, said rotor being operableto control both vertical and horizontal movement of the aircraft, and apropeller supported for rotation about an axis thereof at the front endof the fuselage operable to selectively produce thrust to move theaircraft forward, the method comprising:

transitioning from hover or other in-flight manoeuvre to forward flight;

providing half of an amount of vertical lift needed to maintain analtitude of the aircraft during forward flight on a first side of thefuselage substantially wholly by powering the main helicopter rotor;

providing a remaining half of the amount of vertical lift needed tomaintain the altitude of the aircraft during forward flight on a secondside of the fuselage opposite the first side; and

powering the propeller to provide forward thrust of the aircraft inforward flight.

Transitioning to forward flight may comprise adding forward cyclic tocreate forward thrust from the main helicopter rotor, increasing powerto the propeller as the aircraft beings moving forward and removing theforward cyclic.

Transitioning to forward flight may further comprise the addition ofrearward cyclic to pitch the front end of the fuselage upward.

Powering the main helicopter rotor may provide the remaining half of theamount of vertical lift needed to maintain the altitude of the aircraftduring forward flight on the opposite side of the fuselage.

Alternatively, flowing air around a wing extending laterally from thefuselage on the second side thereof, and powering the main helicopterrotor, together may provide substantially wholly the remaining half ofthe amount of vertical lift needed to maintain the altitude of theaircraft during forward flight.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings, which illustrate a exemplary embodimentsof the present invention:

FIG. 1 is a side elevational view of an aircraft according to a firstembodiment of the present invention.

FIG. 2 is a side elevational view of an aircraft according to a secondembodiment of the present invention.

FIG. 3 is an overhead plan view of the aircraft of FIG. 2.

FIG. 4 is a side elevational view of an aircraft according to a thirdembodiment of the present invention.

FIG. 5 is an overhead plan view of the aircraft of FIG. 4.

FIG. 6 is a side elevational view of an aircraft according to a fourthembodiment of the present invention.

FIG. 7 is a side elevational view of an aircraft according to a fifthembodiment of the present invention.

FIG. 8 is a front elevational view of the aircraft of FIG. 7.

DETAILED DESCRIPTION

As shown in the figures, the aircraft of the present invention has manyfeatures in common with the conventional helicopter. The aircraft 10 hasa fuselage 12 supported atop a pair of skids 14 by braces 15 with a tailboom 18 extending rearward from the fuselage 12. Suitable landing gearother than skids are known to those of skill in the art may besubstituted into the present invention. A main rotor assembly 20consisting of blades 22 extending radially outward from a hub 24 issupported above the fuselage 12. A tail rotor 26 is supported near anend of the tail 18 opposite the fuselage 12. A horizontal stabilizer 17and a vertical stabilizer 19 are supported on the tail boom 18 forstability during flight. These components are all similar in structureand function to those found on a conventional helicopter. The main rotorassembly 20 is controlled by a pilot to provide uniform lift forvertical movement or unbalanced lift to tip the aircraft and inducelateral movement. The tail rotor 26 is driven for rotation to providetransverse thrust to create a moment about the rotor's shaft 28 tooppose a tendancy for the fuselage to rotate about the shaft due to thedriven rotation of the main rotor assembly 20.

The aircraft 10 of the present invention differs from the conventionalhelicopter in that there is provided a propeller 30 on the nose, orfront end, 32 of the fuselage 12. The tractor propeller 30 is driven forrotation in order to produce forward thrust for the aircraft. Whileoperated in the same manner as a conventional helicopter duringvertical, sideways and rearward movement, the improvements of thepresent invention are most apparent during forward flight, in whichoperation of the propeller 30 reduces the reliance on the main rotor 20.

As in conventional helicopters, the rotor assembly is supported atop theshaft 28 that is operatively coupled to a powerplant 34 mounted withinthe fuselage for driven rotation. A typical swashplate assembly 36,known to those of skill in the art, provided on the shaft 28 allowscyclic and collective pitch control of the rotor blades 22. Thecollective pitch control allows the pilot to simultaneously change thepitch of all the blades 22 in order to increase or decrease the angle ofattack of the blades to achieve the desired amount of thrust. The cyclicpitch control allows the pilot to change the pitch of the blades 22depending on their position during rotation, thereby controlling thedirection in which the thrust is applied. In conventional helicopters,creating a difference in the angle of attack from one side of the hub 24to an opposite side by means of the cyclic pitch control creates unevenlift across the rotor assembly 20 which causes the aircraft 10 to tiltand move toward the lowered side having less lift. The same procedure isfollowed when operating the aircraft 10 of the present invention, exceptthat when forward movement is desired, power can be provided to thepropeller 30 to provide forward thrust. This eliminates the need forforward thrust from the main rotor 20, so the aircraft 10 does not haveto be tilted forward like a conventional helicopter during forwardmotion. It should be appreciated however, that from a hovering state,the aircraft 10 may be transitioned to forward cruising in the samemanner as a conventional helicopter.

In a conventional helicopter the cyclic control is used to create morelift during a rear half of the main rotor's rotation nearest the tailthan in a front half of the main rotor's rotation nearest the nose,thereby causing the helicopter to tilt nose down such that the rotationplane of the main rotor is angled from a horizontal orientation. Thiscyclical action is combined with an increase in power and collectivepitch to the rotor so that the angling of the rotor acts to continueproducing lift while adding a forward thrust component. When flyingforward with the present invention, the angle of attack of theretreating blades does not have to be as high, due to the fact that thepropeller is providing thrust for forward cruising. The requiredcollective and cyclic pitches of the blades 22 are therefore less thanrequired for forward flight in a conventional helicopter, as lessoverall thrust is needed from the main rotor 20 and it can be adjustedto only create lift. This decrease in the required angle of attack ofthe blades 22 leads to faster possible forward motion without reachingthe critical angle of attack at which buffeting occurs and beyond whichstalling may take place.

As in a conventional helicopter, the driven rotation of the main rotor20 causes a reactive torque to be exerted on the fuselage 12 in adirection opposite that of the rotor's motion. The tail rotor 26 at theend 38 of the tail 18 is driven for rotation in order to create thrusttransverse to the length of the aircraft 10. This thrust creates amoment which tends to rotate the fuselage 12 about the shaft 28 of themain rotor assembly 20 in a direction opposite the reaction torquecreated by the rotation thereof. The magnitude of the thrust andresulting moment can be controlled by adjusting the pitch of the tailrotor 26. The energy exerted to drive the tail rotor 26 is generallyconsidered to be wasteful, as it does not contribute to the airspeed ofthe aircraft 10, but rather is only used to prevent relative motion ofits components. The vertical stabilizers of conventional helicopterslocated on the tail near the tail rotor are sometimes angled withrespect to a longitudinal axis of the aircraft. During forward flight,this angled arrangement creates a force transverse to the longitudinalaxis which opposes the reaction torque of the main rotor to reducereliance on the tail rotor. Moving forward at higher speeds, thistransverse force may be strong enough to counteract all of this spininducing torque. It should be appreciated that the vertical stabilizer19 of the present invention may be supported in an angled orientation toreduce reliance on the tail rotor 26. As understood by those of skill inthe art, it should be appreciated that the side of the tail on which thetail rotor is supported for rotation is determined by the rotationaldirection of the main rotor and resulting reaction torque exerted on thefuselage. Alternate systems for countering the reaction torque of themain rotor, NOTAR and multiple rotor systems for example, are known tothose of skill in the art and may be applied to the present invention.

As shown in FIG. 1, a first embodiment of the present invention featuresthe propeller supported for rotation within a plane generallyperpendicular to the plane of rotation of the main rotor. To maximizeforward cruising speed, the aircraft may be flown such that the mainrotor 20 rotates about a vertical axis, thereby providing only verticallift. This differs from a conventional helicopter wherein the cycliccontrol is used to create more lift during a rear half of the mainrotor's rotation nearest the tail than in a front half of the mainrotor's rotation nearest the nose, thereby causing the helicopter totilt nose down such that the rotation plane of the main rotor is angledfrom a horizontal orientation and its rotation axis is correspondinglyangled from a vertical orientation. This cyclical action is combinedwith an increase in power and collective to the rotor. These actionsangle and increase the force produced by the main rotor from a verticaldirection such that both vertical lift and forward thrust components arecreated to establish forward cruising of the helicopter. With the mainrotor of the aircraft of the present invention being rotated about avertical axis to create only lift, the propeller is left to provide allof the forward thrust allowing forward flight. The main rotor thus onlyneeds to be provided with the minimum power and collective pitch neededto provide sufficient lift to maintain the altitude of the aircraftduring forward flight. With a minimum amount of collective pitch soapplied and no need to apply additional cyclic pitch to create forwardthrust, the angle of attack of the main rotor is kept relatively lowallowing higher forward speeds to be achieved without experiencingretreating blade stall.

In this first embodiment, there exists a predetermined relationshipbetween the rotational directions of the main rotor and the propeller.Specifically, the main rotor blades 22, at the fowardmost point 48 oftheir rotation, and the blades of the propeller 30, at the uppermostpoint 50 of their rotation, move in the same direction. In other words,the main rotor and propeller, as viewed from above and behindrespectively, both rotate in the same one of either clockwise orcounter-clockwise directions. Test flights with a radio-controlledprototype of this embodiment demonstrated tendencies for the tail tooscillate up and down during forward cruising and the nose to pitchupward when power is provided to the propeller. To counteract thesetendencies, the horizontal stabilizer 17 was increased in size and movedrearward from its original position, which can be seen in theembodiments of FIGS. 3 to 5. The resulting position of the horizontalstabilizer 17 rearward of the tail rotor 26, as shown in FIG. 1, lead tothe elimination of tail oscillation in forward flight, but alone did notcounter the nose-up tendency of the aircraft. The propeller 30 isprovided with a clutch to prevent the nose from lifting during hovering,vertical takeoff or landing and other manoeuvres where forward thrust isnot desired. The clutch allows the propeller to be decoupled from itsdrive source 35 such that no power is delivered to the propeller untilforward thrust is needed. Alternatively, a variable pitch propeller maybe used to allow the pitch to be reduced to zero to reduce the effectsof the propeller's rotation until forward thrust is needed. However, thenose-up problem again becomes an issue once the propeller pitch isincreased or the clutch is engaged to create forward thrust. Asillustrated, this tendency for nose lifting during forward motion wasovercome by angling the horizontal stabilizer 17 downward, from front toback, from a plane parallel to the rotational plane of the main rotor 20and the axis of the tail 18. This creates an angle of attack at thehorizontal stabilizer that produces lift at the tail during forwardflight which acts to counteract the tendency for the nose to lift underdriven rotation of the propeller. Alternatively, the aircraft may betilted slightly forward by the cyclic control in order to create morelift in the rear half of the main rotor's rotation to counteract thisnose-up tendency, similar to the way forward thrust is created forforward flight of a conventional helicopter, except to a lesser degree.In this latter approach, less forward cyclic is applied than in forwardcruising of a conventional helicopter, and so the overall top speed isstill improved as the resulting pitch is not as great. However, asmentioned above, avoiding the application of cyclic pitch and simplydriving the main rotor for rotation about a vertical axis in ahorizontal plane with only enough collective pitch and power needed tomaintain altitude maximizes the top speed by keeping the main rotorangle of attack as low as possible to avoid retreating blade stall andassociated problematic conditions. This is why the first embodimentcorrects the nose-up tendency through providing the horizontalstabilizer with an angle of attack to create lift during forwardcruising rather than through the application of forward cyclic.

The radio controlled prototype of the first embodiment was constructedwith a 2-horsepower motor driving a clutched propeller and a0.5-horsepower motor driving the main rotor. The propeller and mainrotor turn clockwise as viewed from behind and above respectively.Relatively high speed cruising was found to be stable with thecollective pitch at approximately 5 degrees to provide the aircraft'svertical lift to maintain altitude, which corresponded to the amount ofcollective pitch used to maintain a hover. Stability decreased beyondthis value to the point the aircraft was highly unstable at a collectivepitch of 8 degrees. For comparison, a conventional helicopter mightrequire between 6 and 12 degrees of collective pitch during forwardflight to provide enough force for lift and forward thrust, plus cyclicpitch to properly angle the rotor. It was found that angling of thepropeller up to 2 degrees in either direction from a plane perpendicularto the main rotor's rotational plane had little effect on control of theaircraft. An angle of 4 degrees between the horizontal stabilizer and aplane parallel to the tail's axis was found to effectively counteractthe tendency for the nose to lift during forward flight. It should beappreciated that these values are presented as exemplary and may bevaried, for example, in response to other variations in aircraftcharacteristics such as weight distribution.

The aircraft of the first embodiment can be transitioned from hover toforward flight in two different ways due to the presence of thepropeller. One option is to transition in a manner similar to that of aconventional helicopter by increasing power and forward cyclic to themain rotor in order to tilt the aircraft downward at the nose andgenerate forward thrust. Upon attaining a certain amount of forwardspeed, the aircraft experiences transitional lift associated with anincrease in rotor efficiency due to the introduction of fresh air to therotor (recirculation of air through the rotor at the blade tips reducesas the aircraft gains horizontal velocity). At this point, power to thepropeller can be increased to take over the duty of providing forwardthrust and so the power and collective pitch of the main rotor can bereduced and forward cyclic can be removed, thereby tilting the aircraftinto a horizontal orientation for forward cruising. Alternatively, powercan be gradually added to the propeller while hovering to introduce someforward thrust, and once adequate speed for transitional lift has beenattained, power and collective pitch of the main rotor can be reduced.In this case, some forward cyclic may be applied to counteract upwardpitching of the nose as the propeller power is increased and then takenoff as lift created at the tail by the horizontal stabilizer increaseswith forward speed. In either case, the end result is that in forwardcruising only the propeller is used to create forward thrust, therebyminimizing the power and pitch of the main rotor to allow higher topspeeds.

Initiating forward flight in the radio controlled aircraft of the firstembodiment by increasing power to the propeller has been found to induceyaw that can be countered by increasing the power to the tail rotor. Asmentioned above, power to the tail rotor can be reduced as forward speedincreases if the vertical stabilizer is angled to counter the mainrotor's reaction torque on the fuselage.

FIGS. 3 to 5 show second and third embodiments of the present inventionin which the main rotor and propeller, as viewed from above and behindrespectively, rotate in opposite ones of clockwise and counter-clockwisedirections. In other words, the main rotor blades 22, at the fowardmostpoint 48 of their rotation, and the blades of the propeller 30, at theuppermost point 50 of their rotation, move in opposite directions. Testswith radio controlled prototypes of these embodiments found that in sucharrangements, the introduction of forward thrust by the propeller toinduce forward motion was found to cause the aircraft to enter a suddennose dive. However, it was found that tilting of the propeller out ofthe plane perpendicular to the rotational plane of the main rotor couldovercome this nose-diving tendency.

As seen in FIG. 2, the propeller 30 of the second embodiment is notmounted on the nose 32 so as extend in a vertical plane parallel to themain rotor shaft 28 and normal to a longitudinal axis of the fuselage12. The propeller 30 is tilted rearward such that a lowest point in itsrotation 52 is disposed forward of the highest point in its rotation 50.In other words, the axis of the propeller 30 has been rotated downwardabout its front end from a longitudinal axis of the fuselage 12 in avertical plane by a small angle.

A radio controlled prototype of the second embodiment of the presentinvention was able to achieve forward speeds estimated at approximatelytwice what was attainable before the installation of the nose mountedpropeller and a respective powerplant. However, the aircraft wassomewhat difficult to control in its upper velocity range. It iscontemplated however that control at these higher speeds may be improvedwith flight experience as the differences in flight characteristics fromconventional helicopters become more appreciated. This prototype wasfound to fly well at lower speeds with a propeller of relatively finepitch having its rotational plane tilted back approximately twelvedegrees from a vertical orientation and a rotor motor having a powerrating double that of a propeller motor. It should be appreciated thatthe aforementioned details of this prototype have been presented in anexemplary context and that the present invention is not limited to thisparticular arrangement.

Test flights with the radio controlled aircraft of the second embodimenthave shown that a combination of factors, such as the propeller pitch,propeller size, propeller tilt angle, propeller speed and forward airspeed, seem to affect the relationship between the longitudinal axis ofthe fuselage and the line of forward thrust exerted on the aircraft 10.It should therefore be appreciated that by providing control over asleast some of these factors, the orientation or trim of the aircraft canbe controlled during forward flight without increasing the pitch on themain rotor, for example to maintain a parallel relationship between theforward thrust line 54 and the longitudinal axis of the fuselage toallow forward flight in a horizontal orientation. The propeller 30 maybe of the variable pitch type to allow control of its pitch duringflight. The propeller 30 may be pivotally mounted for limited motionabout an axis transverse to the fuselage to allow control over the anglebetween the propeller's plane of rotation and the longitudinal axis ofthe fuselage. This would provide the ability to fine tune the tilt ofthe propeller 30 order to maintain a horizontal orientation of theaircraft 10 during forward flight at particular speeds. The pivotalmounting may be made controllable by the pilot to allow smalladjustments during flight, or could be made to be adjustable only duringgrounded maintenance. The latter option would allow adjustments in theangle of tilt to be made to compensate for exchangeable mounting ofpropellers having different sizes or pitches without having to addanother control device for the pilot in the aircraft. The propeller 30and its respective power plant 35 may be supported on a single pivotalmount to provide this tilt control.

As seen in FIG. 4, the propeller 30 of the third embodiment is also notmounted on the nose 32 so as extend in a vertical plane parallel to themain rotor shaft 28 and normal to a longitudinal axis of the fuselage12. However, unlike the second embodiment, here the propeller 30 istilted forward such that the highest point in its rotation 50 isdisposed forward of the lowest point in its rotation 52. In other words,the axis of the propeller 30 has been rotated upward about its front endfrom a longitudinal axis of the fuselage 12 in a vertical plane by asmall angle. Unlike the first two embodiments there is provided a singlecommon powerplant 40 that has separate rotor and propeller outputs 42and 44 that are operatively connected to the main helicopter rotor andpropeller respectively. A radio controlled prototype of the thirdembodiment of the present invention was found to be easier to controlthan that of the second embodiment but unable to achieve as high a topforward cruising speed as the first embodiment. The aircraft features asingle motor 40 having a driveshaft 44 extending to the nose from thetransmission to drive a variable pitch propeller geared to run at arelatively high speed. In this arrangement, the propeller and variablepitch main and tail rotors all run in sync off the same motor. Duringhover and other manoeuvres not requiring forward thrust, the propelleris kept at zero pitch so as to use a minimum amount of power. Theprototype's propeller plane is angled approximately 3 or 4 degrees froma vertical plane perpendicular to the rotor plane and normal to thefuselage's longitudinal axis. It should be appreciated that theaforementioned details of this prototype have been presented in anexemplary context and that the present invention is not limited to thisparticular arrangement. A higher forward cruising speed relative to thatattainable by conventional helicopter flying techniques before theinstallation of the propeller can be reached by flying the prototype ina tilted back orientation similar to, but to less degree than, agyrocopter.

For forward horizontal cruising the nose is pitched up to tilt theaircraft, including the main rotor, back and dispose the propeller in avertical rotational plane so as to exert forward thrust along thedirection of travel. So to transfer from a hover to forward flight, theaircraft and rotor is pitched nose down by adding forward cyclic tocreate forward thrust from the main rotor, as is done with aconventional helicopter. Once some forward motion is induced, additionalforward thrust is created by increasing the pitch of the propeller. Asthe thrust from the propeller takes over, the cyclic is adjusted toremove the rotor-created forward thrust and rock the aircraft back topitch the nose slightly upward so that the propeller is rotating in agenerally vertical plane. Flown in this tilted orientation, the aircrafthas similar handling characteristics to a gyrocopter and thus is easy tocontrol. Since all of the forward thrust duties are taken over by thepropeller, the pitch on the main rotor is significantly less than inforward cruising of a conventional helicopter, and so the top speed isincreased due to the lower angle of attack on the rotor. The control ofthe aircraft at higher speeds is significantly improved over that of thesecond embodiment, but the top speed is not as high as the firstembodiment due to the tilting back of the rotor in forward cruising. Thesimilarity of this embodiment to a gyrocopter refers only to the slightrearward tilt, or pitching up of the nose, during forward flight and theresulting handling characteristics, and it should be appreciated fromthe above that the main rotor is powered like that of a helicopter.

As illustrated by the above embodiments, the aircraft of the presentinvention may be provided with separate propeller and rotor powerplantsfor driving rotation of the propeller and main rotor respectively, ormay be provided with a common powerplant having separate propeller androtor outputs that are operatively connected to the main helicopterrotor and propeller respectively. When a tail rotor is used to counterthe reaction torque of the main rotor, it may be variable in pitch anddriven off the main rotor in an arrangement typically found inconventional helicopters. To avoid instability in hover due to propellerrotation, a clutched or variable pitch propeller may be used.

The first embodiment teaches that pitching of the nose due to operationof the propeller in forward flight can be countered by creating atendency for the tail to pitch in the opposite direction about alateral, or transverse, axis of the aircraft. Using this concept, it isconceivable that the nose diving tendency of an embodiment in which theblades of the main rotor and propeller move in opposite directions atthe forwardmost and uppermost points of their respective rotationalpaths may be countered by creating a downward force on the tail, forexample by angling a horizontal stabilizer upward from front to rearfrom the tail's longitudinal axis to create a downward force duringforward flight. The fourth embodiment shown in FIG. 6 features such anarrangement where instead of the rotational plane of the propeller beingtilted out of an orientation perpendicular and parallel to the mainrotor's rotational plane and axis respectively (as in the second andthird embodiments), the horizontal stabilizer 17 is angled upward fromfront to rear to counter the nose-diving tendency.

The present invention outlines an aircraft 10 that provides themanoeuvrability of a conventional helicopter with an increasedattainable forward air speed, without the addition of wings which caninterfere with the lift providing capabilities of the main rotor. Inforward cruising, the aircraft of each embodiment uses only thepropeller to create forward thrust. This way the pilot needs only toapply enough power and collective pitch to keep the aircraft fromdropping in altitude, thereby minimizing the angle of attack of therotor blades throughout their rotation. This allows higher forwardcruising speeds than a conventional helicopter to be attained withoutexperiencing retreating blade stall.

It should be appreciated that the addition of other thrust or liftcreating components should not put an aircraft otherwise similar to thepresent invention out of the scope of protection, so long as the mainrotor is being powered to provide essentially the entire amount of liftneeded to maintain the aircraft's altitude during forward cruising. Inother words, adding small components that provide an insignificantfraction of the overall lift to that provided by the rotor in forwardflight would not change the fact that the rotor is being relied upon toprovide substantially wholly the aircraft's lift. So while the presentinvention provides increased speed over conventional helicopters withoutthe need for the wings of a compound helicopter, the addition of wingssmall enough span to avoid a high degree of interference with therotor's downwash should not take the aircraft outside the scope of theclaims.

FIGS. 7 and 8 show a fifth embodiment that has been conceptualized tofurther reduce the angle of attack of the main rotor blades duringforward flight. As described in the background section hereof and wellknown to those of skill in the art, dissymmetry of lift in forwardflight is caused by a difference in the lift created by the advancingand retreating blades. Looking at FIG. 7, blades 22R and 22A are in theretreating and advancing portions of the rotor's rotation respectivelyif the aircraft is considered to be moving in a forward direction asindicated by arrow 54 (the retreating and advancing portions beinghalves of the rotation in which the blade moves away from and toward thedirection of the aircraft's motion respectively). With the lift on theadvancing side exceeding that on the retreating side, the aircraft wouldtend to pitch nose up and roll toward the retreating side without somekind of compensation, typically provided by blade flapping and cyclicfeathering. In this embodiment, the aircraft of the first embodiment hasbeen provided with the addition of a small wing 56 on the retreatingside of the fuselage 12. The wing extends laterally from the fuselage toprovide lift that supplements that of the retreating blade to helpcorrect the unbalanced lift and counteract the rolling tendency. Anylift provided by the wing rearward of the aircraft's pitch axis wouldalso assist in counteracting the nose-up tendency. The wing is keptrelatively small to keep interference with the rotor's downwash low.Using the wing with a blade flapping rotor, where advancing blades areallowed to flap up in response to increased lift to decrease their angleof attack and retreating blades are allowed to flap down in response todecreased lift to increase their angle of attack, the degree to whichthe retreating blades need to flap downward during forward flight couldbe reduced due to the increase in lift on the retreating side by thewing. As a result, the downward flapping could be mechanicallyrestricted to limit the maximum increase in angle of attack provided byblade flapping. The promotion of symmetric lift by the wing could alsoallow a reduction in the degree of cyclic feathering used in forwardflight. Overall, the wing would help keep down the angle of attack ofthe main rotor to allow increased speed in forward flight withoutencountering retreating blade stall.

While the aircraft of the fifth embodiment does feature a wing supportedon the fuselage, it is still distinct from a compound helicopter. Whilein the other embodiments substantially all the vertical lift formaintaining altitude during forward flight is provided by the rotor,here the rotor's lift on the retreating side is supplemented by thewing. This embodiment still avoids the addition of large wings on eachside of the fuselage as found in compound helicopters where lift fromthe pair of wings is necessary to maintain altitude when loading of therotor is significantly decreased. In this embodiment the rotor stillprovides all the vertical lift on the advancing side needed for forwardflight, but uses the small wing to produce some lift on the retreatingside to lessen the degree of increase in angle of attack of theretreating blade to help avoid inducement of retreating blade stall. Itshould be appreciated that the illustrated wing, not extending asubstantial length of the rotor blades, would produce significantly lessvertical drag during vertical manoeuvres than the full size wingsdisposed on both sides of a compound helicopter. Although the fifthembodiment is shown as a modification of the first embodiment, it shouldbe appreciated that the addition of the single wing should present thesame benefits if applied to other embodiments of the present invention.

Since various modifications can be made in my invention as herein abovedescribed, and many apparently widely different embodiments of same madewithin the spirit and scope of the claims without department from suchspirit and scope, it is intended that all matter contained in theaccompanying specification shall be interpreted as illustrative only andnot in a limiting sense.

1. An aircraft comprising: a fuselage having a front end and alongitudinal axis; a main helicopter rotor supported for rotation aboutan axis thereof on top of the fuselage, said rotor being operable tocontrol both vertical and horizontal movement of the aircaft; apropeller supported for rotation about an axis thereof at the front endof the fuselage operable to selectively produce thrust to move theaircraft forward; and at least one powerplant supported on the fuselage;the main rotor and propeller each being operatively connected to the atleast one powerplant for selective driven rotation thereby; wherein onat least one side of the fuselage, vertical lift is providedsubstantially wholly by the main helicopter rotor during forwardcruising.
 2. The aircraft according to claim 1 wherein the at least onepowerplant comprises a propeller powerplant and a rotor powerplant, thepropeller and main helicopter rotor being operatively connected to thepropeller and rotor powerplants respectively.
 3. The aircraft accordingto claim 1 wherein the at least one powerplant comprises a commonpowerplant having a rotor output and a propeller output, the propellerand main helicopter rotor being operatively connected to the propellerand rotor outputs respectively.
 4. The aircraft according to claim 1wherein the propeller is adjustable in pitch.
 5. The aircraft accordingto claim 1 further comprising a clutch operable to couple and decouplethe propeller and the at least one powerplant.
 6. The aircraft accordingto claim 1 wherein the main helicopter rotor, at a forwardmost point ofits rotation, and the propeller, at an uppermost point in its rotation,move in a common direction.
 7. The aircraft according to claim 6 furthercomprising a horizontal stabilizer supported rearward of the fuselageand extending obliquely with respect to the longitudinal axis of thefuselage so as to extend downward from front to rear.
 8. The aircraftaccording to claim 7 wherein the horizontal stabilizer is disposedrearward of a tail rotor supported for rotation rearward of thefuselage.
 9. The aircraft according to claim 6 wherein the propeller issupported for rotation in a plane generally perpendicular to arotational plane of the main helicopter rotor.
 10. The aircraftaccording to claim 1 wherein the main helicopter rotor, at a forwardmostpoint in its rotation, and the propeller, in an uppermost point in itsrotation, move in opposite directions.
 11. The aircraft according toclaim 10 further comprising a horizontal stabilizer supported rearwardof the fuselage and extending obliquely with respect to the longitudinalaxis of the fuselage so as to extend upward from front to rear.
 12. Theaircraft according to claim 11 wherein the horizontal stabilizer isdisposed rearward of a tail rotor supported for rotation rearward of thefuselage.
 13. The aircraft according to claim 10 wherein the propellerbeing supported for rotation in a plane transverse to the fuselage, saidplane being inclined with respect to the longitudinal axis of thefuselage so as to extend upward from front to rear with saidlongitudinal axis horizontally oriented.
 14. The aircraft according toclaim 10 wherein the propeller being supported for rotation in a planetransverse to the fuselage, said plane being inclined with respect tothe longitudinal axis of the fuselage so as to extend downward fromfront to rear with said longitudinal axis horizontally oriented.
 15. Theaircraft according to claim 1 further comprising a wing extendinglaterally from one side of the fuselage to counter dissymmetry of liftof the main helicopter rotor during forward flight.
 16. A method offlying an aircraft comprising a fuselage having a front end and alongitudinal axis, a main helicopter rotor supported for rotation aboutan axis thereof on top of the fuselage, said rotor being operable tocontrol both vertical and horizontal movement of the aircraft, and apropeller supported for rotation about an axis thereof at the front endof the fuselage operable to selectively produce thrust to move theaircraft forward, the method comprising: transitioning from hover orother in-flight manoeuvre to forward flight; providing half of an amountof vertical lift needed to maintain an altitude of the aircraft duringforward flight on a first side of the fuselage substantially wholly bypowering the main helicopter rotor; providing a remaining half of theamount of vertical lift needed to maintain the altitude of the aircraftduring forward flight on a second side of the fuselage opposite thefirst side; and powering the propeller to provide forward thrust of theaircraft in forward flight.
 17. The method according to claim 16 whereintransitioning to forward flight comprises adding forward cyclic tocreate forward thrust from the main helicopter rotor, increasing powerto the propeller as the aircraft beings moving forward and removing theforward cyclic.
 18. The method according to claim 17 whereintransitioning to forward flight further comprises adding rearward cyclicto pitch the front end of the fuselage upward.
 19. The method accordingto claim 16 wherein powering the main helicopter rotor providessubstantially wholly the remaining half of the amount of vertical liftneeded to maintain the altitude of the aircraft during forward flight onthe opposite side of the fuselage.
 20. The methods according to claim 16wherein flowing air around a wing extending laterally from the fuselageon the second side thereof, and powering the main helicopter rotor,together provide substantially wholly the remaining half of the amountof vertical lift needed to maintain the altitude of the aircraft duringforward flight.